text: Fick's second law predicts how diffusion causes the concentration to change with respect to time. It is a partial differential equation which in one dimension reads:
  where
  *  is the concentration in dimensions of , example mol/m;  is a function that depends on location  and time 
  *  is time, example s
  *  is the diffusion coefficient in dimensions of , example m/s
  *  is the position, example m
  In two or more dimensions we must use the Laplacian , which generalises the second derivative, obtaining the equation
  Fick's second law has the same mathematical form as the Heat equation and its fundamental solution is the same as the Heat kernel with diffusion coefficient :